Mastering Load Balancing: 5 Core Strategies and How to Choose the Right One

What Is Load Balancing?

Load balancing is the process of using a single unified entry point to collect traffic and then redistribute it, similar to a navigation app that selects a limited number of optimal routes to spread vehicle flow.

In software systems, a load balancer prevents uneven traffic distribution and overloaded nodes by acting as a “traffic navigator”, but unlike navigation it makes routing decisions automatically based on defined strategies.

Common Load‑Balancing Strategies

1. Round‑Robin

Distributes requests evenly in a cyclic order. Example code is illustrated in the image below.

2. Weighted Round‑Robin

Extends round‑robin by assigning a weight to each server, allowing more powerful nodes to receive more traffic. The image demonstrates the algorithm and its weight‑based selection process.

The following diagram shows the weight calculation and selection flow.

3. Least Connections

Selects the server with the fewest active connections at the moment, providing dynamic balancing based on real‑time load.

4. Fastest Response

Routes traffic to servers that have responded most quickly in recent measurements, effectively a weighted approach based on response time.

5. Hash‑Based

Uses a hash of a client identifier (commonly the source IP) to consistently map a client to a particular server, ensuring session affinity. The simple modulo hash is shown below.

Pros, Cons, and Use‑Cases

Each algorithm balances simplicity against performance. Simple methods are easy to implement, while more sophisticated combinations or data‑driven predictions can achieve better results at the cost of complexity.

Health Checks for High Availability

To keep a load balancer reliable, health‑checking mechanisms remove unhealthy nodes from the pool. Common checks include:

HTTP probing : Send GET/POST to a fixed URL and evaluate status code or response content.

TCP probing : Perform a TCP three‑way handshake and immediately reset the connection to release resources.

UDP probing : Send a UDP packet and consider the service healthy if no error response is received.

Conclusion

Load balancing distributes requests across multiple units according to defined rules, enabling horizontal scaling and higher availability while improving resource utilization.